DO Now:
You find a sedimentary rock that has
one graded bed. Describe how you
know which layer of the graded bed is
formed last?
SOIL EQ: WHAT IS SOIL AND WHAT ARE
THE COMPONENTS OF SOIL?
EQ:
What is soil and what are the
components of soil?
GPS: S6E5 Students will investigate the scientific view of how Earth’s surface is
formed
f. explain that soil is made of weathered rock and decomposed organic matter
SOIL
WHAT IS SOIL?
Soil is the portion of Earth’s surface that
consists of organic matter mixed with
sediment, air, and water.
Soil is a natural resource that is needed to
support life on Earth.
SOIL
There is a big difference between “dirt” and
“soil.”
 We use the word “dirt” to mean particles and
dust that we don’t want around.
 Soil contains humus as well as particles of
weathered rock including sand, silt, and clay.
 Water, air, and living organisms are also
important components of soil.

SOIL
COMPONENTS OF SOIL
Organic Material
Humus – the material that
is produced by the
bacterial decay of plant
and animal matter
(organic matter).

COMPONENTS OF SOIL

Sediments – weathered rock
Sand
Silt
Clay
COMPONENTS OF SOIL

Water, air, and
living organisms
SOURCE OF SOIL

Soil is made from weathered rock fragments,
therefore the type of soil that forms depends
on the type of rock that weathers.
SOIL FORMATION
PARENT ROCK
•
The parent rock
is the rock that is
weathered to
create the soil.
Ex: If granite
weathers to make
soil then granite
is the parent rock
of that soil.
SOIL FORMATION


Soil is part of the rock cycle.
Factors that affect soil formation include:





climate,
type of parent rock or mineral,
presence of living organisms,
topography, and
time.
FACTORS THAT AFFECT SOIL FORMATION
1.
2.
3.
Parent Rock – affects type of soil and rate
at which the soil develops
Climate - soils form more quickly in warm,
wet environments where weathering of
parent rock is quicker/also affects the
organic makeup of the soil
Living Organisms – soil forms more quickly
with plants, animals, bacteria, and fungi to
assist with weathering/also affects the
organic makeup of the soil
FACTORS THAT AFFECT SOIL FORMATION
(CONTINUED)
4. Topography – Steepness, shape, and length of
slope are important because they influence
the rate at which water flows into or off the
soil, affecting the rate of soil formation.
5. Time - The longer a soil surface has been
exposed to soil forming agents like rain and
growing plants, the greater the development of
the soil. Soils take thousands or millions of
years to form.
LAYERS OF SOIL


A soil profile is a cross-section that shows the
different layers (or horizons) of soil in the ground.
Young (or immature) soil does not have as many
layers as mature soil.
SOIL PROFILE

The soil profile is
a cross section
that shows the
different layers
of soil.
CHARACTERISTICS OF THE HORIZONS OF SOIL

Horizon O – dark layer of
decaying sticks, leaves,
and some humus.

Horizon A – dark layer
called topsoil that is
humus and small pieces
of rock. This layer is
home to animals. (bugs
and worms)
CHARACTERISTICS OF THE HORIZONS OF SOIL

Horizon B – layer called subsoil made of weathered rock
pieces, clay and rocks.

Horizon C – layer of
weathered rock pieces and
minerals. (Parent Rock)

Horizon D – layer of solid
rock, called bedrock.
WHAT IS HUMUS?

Remember – Humus is the material that is
produced by the bacterial decay of plant and
animal matter (organic matter).
WHAT IS BEDROCK?

Bedrock is the layer of solid rock formations
beneath the soil.
TYPES OF SOIL


There are 12 soil types, or orders.
Soil classification is based on the
following properties:









How much the soil horizons are developed
Composition of different soil horizons
Amount of organic material
Amount of weathering and leaching of
minerals
Presence of calcium carbonate subsurface
Location below grasslands or forests
Presence of clay that shrinks and swells when
mixed with water
Presence of permafrost
Presence of volcanic ash
TYPES OF SOIL
GENERAL TERMS FOR SOIL TYPES
Focus on three types of soil: pedocal, pedalfer,
and laterite.



Pedocal forms in dry or semi-dry climates and is
rich in calcium.
Pedalfer forms in humid climates and is high in
aluminum and iron.
Laterite forms in tropical climates that have a lot
of rains so it is leached of most of its elements.
SOIL PROFILES
SOIL TYPES
EROSION AND AGRICULTURE
Soil that contains a
mixture of sediments,
humus, air, and water
is ideal for growing
crops.
 More soil is lost each
year through erosion
than is formed by
nature.



This soil profile shows
the layer of topsoil on a
farm in Iowa.
Due to farming, Iowa’s
average topsoil depth
has decreased from
14–18 inches to only
6–8 inches.
SOIL FORMATION
Factors that affect soil formation
How?
climate
soil forms more quickly in wet, warm
environments than in cold, dry ones
type of parent rock or
mineral
some types of rocks weather and
become soil faster than others
presence of living
organisms
parent rocks and minerals influence
color, texture, and chemistry of soil
soil formation happens more quickly
in the presence of living organisms
decaying parts of plants and animals
increase humus in soil
SOIL FORMATION
Factors that affect soil formation
How?
topography
the steeper the slope, the more
rocks are exposed to weathering, the
faster rocks and minerals break
down
soil forms more quickly on top of
other soil
more surface area exposed, the
faster a rock weathers
time
forming soil can take thousands to
millions of years; but can be faster
depending on the above factors